In the previous parts of the series we learned about AOP concepts and the need for using AOP in large scale projects and I introduced CodeIgniter's hooks as a convenient mechanism for creating AOP functionality from scratch. In this part I'll show you how to use both XML and comment-based techniques to create custom AOP functionality when a dedicated AOP framework is not available.

They start with the XML configuration that defines a few aspects and pointcuts for the application. This is then read in via the "applyBeforeAspects" and the aspects that should be executed first are extracted, loaded and run. Following this, they take the other approach - based on docblock comments - and pull in the comments (the @before and @after tags) and load/execute the aspects that way instead.